This invention concerns a magnetic apparatus for anchoring ferromagnetic parts suitable in particular, but not exclusively, for use in large permanent magnet power-lifts, of the type in which the magnetic activation and deactivation of the apparatus is achieved by reversing the polarity of a group of magnets by means of electric inductors or coils which surround the magnets themselves, and which are fed with pulses of current in one direction and, respectively, in the opposite direction to the first. In all cases of magnetic anchorage of ferrous loads having a deformed and/or rough contact surface, it is essential to be able to make use of magnetic apparatuses with a work or anchoring surface which is as limited as possible, in its external development, and of isometric configuration, while maintaining a high power or magnetic performance of the apparatus itself; this is particularly important, for example, in the field of large power-lifts for very large and heavy parts, where permanent-magnet lifting units have not until now been able to offer the required power and a high degree of operational reliability.
The concept of limiting the external development of the apparatus has been included in a number of German regulations, especially for large circular power-lifts of the electromagnetic type; according to this regulation, the theoretical magnetic power of the apparatus--in order to ensure the utmost operational reliability--should be declassed in direct proportion to the width and length of the magnetic work surface of the power-lift, that is, to the external development of the apparatus itself. In other words, it is important to make the peripheral conformation of the apparatus isometric (central symmetry) in order to enable the apparatus to operate uniformly, that is to say, without having to resort to obliged positioning of the latter with respect to the load to be lifted or to the parts to be anchored.
In magnetic power-lifts, it is also important that the theoretical power of the apparatus is absorbed as far as possible by the load, or by the parts to be lifted and that it is not diverted along flux paths which do not affect the part or parts to be anchored. In other words, it is essential that the maximum of induction or the maximum of flux provided by the apparatus is short-circuited by the minimum thickness of ferromagnetic material in order to ensure satisfactory anchorage under the most varied working conditions. It is also important, with the same power actually provided, that the weight and the cost of the apparatus are as low as possible. Magnetic anchoring apparatuses of the permanent magnet type are generally known, also by previous patents of the applicant, in which the activation and deactivation of the apparatus occurs by reversing the polarity of some of the magnets which make up its circuit. However, in such apparatuses of the known type, due either to the particular conformation of the magnetic circuit, or to the disposition and distribution of the masses of magnetic material itself, and to other structural and design characteristics, it is not possible to achieve a symmetrical conformation of the apparatus, according to the above-mentioned principles, without loss of a considerable reduction in the power provided by the apparatus, resulting in limitations in its use.
A scope of this invention is to provide a magnetic anchoring apparatus, of the type previously mentioned, which is capable of satisfying the specified requirements, and in particular an apparatus of such a kind, in relation to other conventionally constructed equipment, having equal theoretical power, as to enable total short-circuiting of the available magnetic flux, in the least possible thickness of the load or of the ferromagnetic parts to be anchored.
A further scope of the invention is to provide an apparatus as mentioned above, in which the area of its magnetic or anchoring surface is substantially symmetric with respect to a central axis of the apparatus itself (principle of isometry), which has pole pieces with very limited volumes and, therefore, weights and in which the leakage flux is drastically reduced or almost eliminated.